Ecology

ABSTRACT “ Candidatus Accumulibacter” and total bacterial community dynamics were studied in two lab-scale enhanced biological phosphorus removal (EBPR) reactors by using a community fingerprint technique, automated ribosomal intergenic spacer analysis (ARISA). We first evaluated the quantitative capability of ARISA compared to quantitative real-time PCR (qPCR). ARISA and qPCR provided comparable relative quantification of the two dominant “ Ca . Accumulibacter” clades (IA and IIA) detected in our reactors. The quantification of total “ Ca . Accumulibacter” 16S rRNA genes relative to that from the total bacterial community was highly correlated, with ARISA systematically underestimating “ Ca . Accumulibacter” abundance, probably due to the different normalization techniques applied. During 6 months of normal (undisturbed) operation, the distribution of the two clades within the total “ Ca . Accumulibacter” population was quite stable in one reactor while comparatively dynamic in the other reactor. However, the variance in the clade distribution did not appear to affect reactor performance. Instead, good EBPR activity was positively associated with the abundance of total “ Ca . Accumulibacter.” Therefore, we concluded that the different clades in the system provided functional redundancy. We disturbed the reactor operation by adding nitrate together with acetate feeding in the anaerobic phase to reach initial reactor concentrations of 10 mg/liter NO 3 -N for 35 days. The reactor performance deteriorated with a concomitant decrease in the total “ Ca . Accumulibacter” population, suggesting that a population shift was the cause of performance upset after a long exposure to nitrate in the anaerobic phase.

ABSTRACT To investigate the fine-scale diversity of the polyphosphate-accumulating organisms (PAO) “ Candidatus Accumulibacter phosphatis” (henceforth referred to as “ Ca. Accumulibacter”), two laboratory-scale sequencing batch reactors (SBRs) for enhanced biological phosphorus removal (EBPR) were operated with sodium acetate as the sole carbon source. During SBR operations, activated sludge always contained morphologically different “ Ca . Accumulibacter” strains showing typical EBPR performances, as confirmed by the combined technique of fluorescence in situ hybridization (FISH) and microautoradiography (MAR). Fragments of “ Ca. Accumulibacter” 16S rRNA genes were retrieved from the sludge. Phylogenetic analyses together with sequences from the GenBank database showed that “ Ca. Accumulibacter” 16S rRNA genes of the EBPR sludge were clearly differentiated into four “ Ca. Accumulibacter” clades, Acc-SG1, Acc-SG2, Acc-SG3, and Acc-SG4. The specific FISH probes Acc444, Acc184, Acc72, and Acc119 targeting these clades and some helpers and competitors were designed by using the ARB program. Microbial characterization by FISH analysis using specific FISH probes also clearly indicated the presence of different “ Ca. Accumulibacter” cell morphotypes. Especially, members of Acc-SG3, targeted by probe Acc72, were coccobacillus-shaped cells with a size of approximately 2 to 3 μm, while members of Acc-SG1, Acc-SG2, and Acc-SG4, targeted by Acc444, Acc184, and Acc119, respectively, were coccus-shaped cells approximately 1 μm in size. Subsequently, cells targeted by each FISH probe were sorted by use of a flow cytometer, and their polyphosphate kinase 1 ( ppk1 ) gene homologs were amplified by using a ppk1 -specific PCR primer set for “ Ca. Accumulibacter.” The phylogenetic tree based on sequences of the ppk1 gene homologs was basically congruent with that of the 16S rRNA genes, but members of Acc-SG3 with a distinct morphology comprised two different ppk1 genes. These results suggest that “ Ca. Accumulibacter” strains may be diverse physiologically and ecologically and represent distinct populations with genetically determined adaptations in EBPR systems.

ABSTRACTThe orderRickettsiales(Alphaproteobacteria) is a well-known group containing obligate endocellular prokaryotes. The order encompasses three families (Rickettsiaceae,Anaplasmataceae, andHolosporaceae) and a fourth, family-level cluster, which includes only one candidate species, “CandidatusMidichloria mitochondrii,” as well as several unnamed bacterial symbionts. The broad host range exhibited by the members of the “CandidatusMidichloria” clade suggests their eventual relevance for a better understanding of the evolution of symbiosis and host specificity ofRickettsiales. In this paper, two new bacteria belonging to the “CandidatusMidichloria” clade, hosted by two different strains of the ciliate protistEuplotes harpa, are described on the basis of ultrastructural observations, comparative 16S rRNA gene sequence analysis, and an estimation of the percentage of infection. Ultrastructure of these bacteria shows some unusual features: one has an electron-dense cytoplasm, and the other one lacks a symbiosomal membrane. The latter was up to now considered an exclusive feature of bacteria belonging to the familyRickettsiaceae. 16S rRNA gene phylogenetic analysis unambiguously places the new bacteria in the “CandidatusMidichloria” clade, although their phylogenetic relationships with other members of the clade are not clearly resolved. This is the first report of a ciliate-borne bacterium belonging to the “CandidatusMidichloria” clade. On the basis of the data obtained, the two bacteria are proposed as two new candidate genera and species, “CandidatusAnadelfobacter veles” and “CandidatusCyrtobacter comes.”

ABSTRACTHere we investigated the bacterial endosymbionts of weevils of the genusCurculio. From all four species ofCurculioweevils examined, a novel group of bacterial gene sequences were consistently identified. Molecular phylogenetic analyses demonstrated that the sequences formed a distinct clade in theGammaproteobacteria, which was not related to previously known groups of weevil endosymbionts such asNardonellaspp. andSodalis-allied symbionts. In situ hybridization revealed that the bacterium was intracellularly harbored in a bacteriome associated with larval midgut. In adult females, the bacterium was localized in the germalia at the tip of each overiole, suggesting vertical transmission via ovarial passage. Diagnostic PCR surveys detected high prevalence of the bacterial infection in natural host populations. Electron microscopy identified the reduced cell wall of the bacterial cells, and the bacterial genes exhibited AT-biased nucleotide composition and accelerated molecular evolution, which are suggestive of a long-lasting endosymbiotic association. On the basis of these results, we conclude that the novel endocellular bacteria represent the primary symbiont ofCurculioweevils and proposed the designation “CandidatusCurculioniphilus buchneri.” In addition to “Ca.Curculioniphilus,” we identifiedSodalis-allied gammaproteobacterial endosymbionts from the chestnut weevil,Curculio sikkimensis, which exhibited partial infection frequencies in host insect populations and neither AT-biased nucleotide composition nor accelerated molecular evolution. We suggest that suchSodalis-allied secondary symbionts in weevils might provide a potential source for symbiont replacements, as has occurred in an ancestor ofSitophilusgrain weevils.

ABSTRACTAs polyphagous, holometabolous insects, tephritid fruit flies (Diptera: Tephritidae) provide a unique habitat for endosymbiotic bacteria, especially those microbes associated with the digestive system. Here we examine the endosymbiont of the olive fly [Bactrocera oleae(Rossi) (Diptera: Tephritidae)], a tephritid of great economic importance. “CandidatusErwinia dacicola” was found in the digestive systems of all life stages of wild olive flies from the southwestern United States. PCR and microscopy demonstrated that “Ca.Erwinia dacicola” resided intracellularly in the gastric ceca of the larval midgut but extracellularly in the lumen of the foregut and ovipositor diverticulum of adult flies. “Ca.Erwinia dacicola” is one of the few nonpathogenic endosymbionts that transitions between intracellular and extracellular lifestyles during specific stages of the host's life cycle. Another unique feature of the olive fly endosymbiont is that unlike obligate endosymbionts of monophagous insects, “Ca.Erwinia dacicola” has a G+C nucleotide composition similar to those of closely related plant-pathogenic and free-living bacteria. These two characteristics of “Ca.Erwinia dacicola,” the ability to transition between intracellular and extracellular lifestyles and a G+C nucleotide composition similar to those of free-living relatives, may facilitate survival in a changing environment during the development of a polyphagous, holometabolous host. We propose that insect-bacterial symbioses should be classified based on the environment that the host provides to the endosymbiont (the endosymbiont environment).